1. Field of the Invention
The present invention relates to a toner concentration measuring method, a toner concentration measuring apparatus and an image forming apparatus employing the same, and a toner concentration measuring method and a toner image measuring instrument by which the concentration of toner in solvent is detected and an image forming apparatus employing the same.
2. Description of the Related Art
Conventionally, a remaining ink amount detecting apparatus for liquid development is required only to detect presence or absence of ink and represent it in a binary value. Thus, a method wherein a voltage is applied to an electrode pair to measure a capacitance between the electrodes is disclosed, for example, in Japanese Patent Laid-Open No. Hei 2-169259. Also another method wherein an amount of transmission light is measured using a light emitting diode and a light receiving element is disclosed, for example, in Japanese Patent Laid-Open No. Hei 6-241996.
However, the conventional methods described above cannot be used to measure the concentration of toner in solvent. Also a method of measuring the concentration of toner in solvent is conventionally known. According to the conventional method, for example, a light emitting diode is used to read an analog variation of the amount of transmission light, and an ac voltage is applied to an electrode pair placed in solvent to measure the concentration of toner from a variation value of the capacitance between the electrodes.
The conventional method just described has a problem of an accuracy of measurement. Where light is used to measure the concentration, the light is attenuated significantly while it passes through the solvent. Consequently, a light emitting element having a very large amount of light emission must be used. However, the amount of light which can be received by the light receiving element is still small, and consequently, the accuracy in measurement of the concentration based on the received mount of light is low. Further, if the light emitting element or the light receiving element is placed in the solvent, the light emitting face or the light receiving face must be kept clean, or if the light emitting element or the light receiving element is located outside a member in which the solvent is accommodated, then a light transmitting wall of the member must be kept clean. If a light transmitting portion becomes soiled, then the accuracy in measurement is further deteriorated.
The conventional method has another problem in that a conventional technique for electric measurement cannot be applied as it is. This is because, even though the conductivity or the capacitance of the solvent can be measured, it is impossible to extract only the concentration of the toner from the measured conductivity or capacitance.